This application is a 371 of PCT/JP98/05928
The present invention relates to a blood circulation assisting device using a continuous flow blood pump for blood feeding assistance and a diagnosis device for evaluating blood circulation state in an organism using the same.
Pulsatile blood flow pumps for use in blood circulation assistance include positive-displacement pumps such as a diaphram type and a pusher plate type. The ejection of the positive-displacement pump is controlled so as to satisfy the needs of an organism by being driven with a complete-filling complete-ejection mode. However, the positive-displacement pumps face difficulty in the development as an artificial heart because their structure is complicated.
On the other hand, continuous flow blood pumps have been developed for the purpose of assisting blood circulation in organism. They include not only typical types such as a centrifugal pump, an axial flow pump and a mixed flow pump, but ones which drive out blood by using a rotor, a precessional moving body, a swaying moving body, oscillations or undulations. Since their structure is simple and they can be manufactured at low cost, they show greater promise than the positive-displacement pumps. However, it is said that the continuous flow blood pumps are more difficult to control than the positive-displacement pumps.
In order to perform the circulation assistance satisfying the needs of organism, a method for monitoring one or the combination of blood pressure, blood flow rate of a pump or an organism, sympathetic nerve activity and venous oxygen saturation by using a specific sensor has been invented. However, sensors that can endure a continuous use for a long period of time without a replacement have not been developed.
In order to eliminate the use of any specific sensor, the following method for controlling the drive of the continuous flow blood pump has been proposed. The method employs a mean motor current consumption and a hydraulic performance of the pump in use to estimate the pump flow rate, thereby maintaining a constant flow rate. In other words, in the continuous flow blood pump, the correlation can be obtained between a pump speed, a generated pressure head (pressure), a pump flow rate and a motor current consumption. Therefore, when the pump speed and the motor current consumption are known, the generated pressure head and flow rate of the pump can be estimated. In addition, the pump speed and the motor current consumption can be taken and used as internal data of the motor without using any specific sensor. As a result, the pump speed can be controlled with a simple structure so as to maintain the constant flow rate. (Cf., xe2x80x9cControl of Centrifugal Blood Pump Based on the Motor Currentxe2x80x9d, Tatsuhiko Iijima, et. al., Artificial Organs Vol. 21, No. 7, 1997, Japanese Society of Artificial Organs.)
However, the controlling method in which the pump flow rate is estimated by a mean motor current consumption and a hydraulic performance of the pump in use, thereby maintaining a constant flow rate, has several problems.
Firstly, the controlling method cannot perform an appropriate blood circulation assistance in an organism. The blood flow rate needed by an organism varies very much according to the individual""s condition. For example, size, state of activity and circulated blood volume of the individual have influence on the optimal blood flow rate. Specifically, the usual cardiac output of an infant having a body weight of 10 kg is approximately 1 L/min, while the cardiac output of an adult during exertion may exceed 10 L/min. Therefore, the controlling method of merely maintaining the constant pump flow rate is not suitable for the appropriate blood circulation assistance in an organism.
Secondly, since the motor current consumption is influenced by a kinematic viscosity of the liquid during feeding, when the liquid is blood, for example, its change in character causes a large error in estimating the pump flow rate. What influences the kinematic viscosity of blood are factors such as the number of red cell (or hematocrit value), serum lipids value or serum whole protein value. These values fluctuate according to the physiological state of an organism. However, there is no method developed for continuously monitoring the kinematic viscosity or component concentration of blood. Thus, it is difficult to achieve a method for controlling a blood feeding so as to obtain the desired flow rate free from the influence by the blood characteristic such as the kinematic viscosity.
It is an object of the present invention to solve the problems of the prior art mentioned above and to provide a blood circulation assisting device using a continuous flow blood pump that realizes an appropriate circulation assistance matching a blood circulation state in an organism as well as the desired flow rate without using any specific sensor for monitoring blood character.
The blood circulation assisting device according to the present invention includes a continuous flow blood pump made of a non-displacement-type pump for blood feeding assistance, a blood removing pipe having one end attachable to a blood removal site in an organism and the other end connected to an inflow portion of the continuous flow blood pump, a blood feeding pipe having one end attachable to a blood feed site in the organism and the other end connected to an outflow portion of the continuous flow blood pump. Blood is removed via the blood removing pipe and driven out via the blood feeding pipe by the continuous flow blood pump so as to attain a predetermined flow rate. The blood circulation assisting device further includes a flow rate detection means for directly or indirectly obtaining data corresponding to a blood flow rate flowing through the continuous flow blood pump, a flow rate amplitude detection means for obtaining, from an output of the flow rate detection means, data corresponding to a fluctuation amplitude of the flow rate, and a means for adjusting an output of the flow rate amplitude detection means to a predetermined value.
With the above configuration, the flow rate amplitude detection means provides an output according to the blood circulation state in an organism, so circulation assistance matching the blood circulation state in the organism can be achieved easily by the control based on the output. In order to show more clearly that the device with the above configuration can achieve the object of the present invention, clinical backgrounds regarding blood circulation assistance and more detailed effects of the device with the above configuration are explained in the following.
When a continuous flow blood pump is under usual operation, it drives out a continuous flow, and its consumption current does not show pulsation. On the other hand, unless the heart of an organism is under cardiac arrest or an arrhythmic state close to the cardiac arrest, it generates a pulsatile flow. Accordingly, when the continuous flow blood pump is used for circulation assistance in an organism, a pump flow that initially is a continuous flow is influenced by a pulsation of native cardiac output, and begins to show pulsation. As a result, current waveform of the motor, which drives the pump, also shows pulsation.
We noted this specific pulsation appeared when used in an organism, and found that an appropriate circulation assistance was made possible by referring to a pulsation of consumption current value rather than to a mean value of motor current consumption.
In the following, with respect to blood circulation assistance, xe2x80x9ctotal assistancexe2x80x9d refers to the case where cardiac output of an organism is not seen, and the blood pump drives out all the blood. However, this does not necessarily mean cardiac arrest, so the heart of the organism may generate some pressure. On the other hand, xe2x80x9cpartial assistancexe2x80x9d refers to the state where the cardiac output of an organism is apparent, and at the same time the blood pump also drives out blood.
{circle around (1)} t-point
When the pump speed is low, native cardiac out put surpasses pump output, and blood circulates in an organism with pulsatile flow. Therefore, the consumption current waveform of the motor also shows pulsation. As the pump speed becomes higher, the pump output comes close to the native cardiac output, and then comes to the same level. This point is called t-point (originating from a term xe2x80x9ctotal assist pointxe2x80x9d) in the present invention. When the pump speed is further raised above the t-point, pump output exceeds native cardiac output and the native cardiac output disappears, which means that the assist condition changes from partial to total assistance. Thus, the circulation in the organism changes from pulsatile to continuous flow. Consequently, the pulsation of the motor current waveform decreases gradually.
This is shown in the graph of FIG. 1. This graph illustrates an example of a relationship between the motor speed and each monitoring indicator. Since this graph will be explained in detail later, only an index of current amplitude is described here. The index of current amplitude is a value obtained by dividing the amplitude of current fluctuation with simultaneous mean current value. The reason the index of current amplitude is used is as follows.
The mean value of motor current consumption increases along with the speed increase. Therefore, current consumption amplitude also tends to increase along with the speed increase, even if the condition of an organism does not change. Consequently, it is difficult directly to detect the alteration of pulsatile flow of the circulation in the organism from the alteration of amplitude of current fluctuation. In other words, the absolute value of the amplitude of current fluctuation is influenced by the motor speed change. In order to detect only the alteration of pulsatile flow of the circulation in the organism, it is desirable that the index of current amplitude is used as an indicator. As is described in the following, when the alteration of pulsatile flow is detected with a flow meter, which directly measures blood flow rate rather than motor current, such an indicator is unnecessary in essence.
The t-p point and t-i point correspond to t-point mentioned above. The points at which the assist condition of the pump turns from partial to total assistance are distinguished based on an identification technique. Thus, the point that is identified by systolic aortic pressure and systolic left ventricular pressure is termed the t-p point, and the point that is identified by the index of current amplitude is termed the t-i point. As is described below, these two points substantially match. The t-point in this section refers to the t-i point.
As is clearly shown in FIG. 1, the t-point is a specific point that clearly appears as the motor speed increases.
{circle around (2)} s-point
As pump speed increases, a sucking phenomenon starts occurring at the blood removal site. In general, the sucking occurs intermittently, corresponding to pulsation of the heart in an organism, and causing pulsation in blood flow in the pump. In the case of appropriate blood removal by the pump and not being short of blood volume, the sucking becomes apparent at the pump speed higher than the t-point, that is still higher than the speed when the circulation in the organism and the pump come extremely close to the continuous flow. Thus, the amplitude of the fluctuation of consumption current waveform becomes the smallest when coming close to a continuous flow, and becomes larger again when the sucking becomes distinct. This point is called s-point (originating from a xe2x80x9csucking pointxe2x80x9d) in the present invention. As is shown in FIG. 1, the index of current amplitude becomes larger beyond the s-point.
As is described above, when the relationship between motor speed and current fluctuation amplitude is shown with motor speed and the index of current amplitude (a value obtained by dividing the amplitude with mean current value), there are two specific points, that is, the t-point at which the circulation assistance changes from partial to total assistance and the s-point at which the pulsation of blood flow in the pump starts occurring due to sucking.
As is mentioned above, the t-point is the point at which the circulation assistance by the pump changes from partial to total assistance. In order to make this total assistance possible, it is necessary that the pump can generate a pressure head sufficient to drive out the entire venous return volume and maintain flow rate. The pressure head is a pressure difference between inlet and outlet tubes of the pump and heavily depends on the blood pressure of the feeding side in an organism. Since this blood pressure is defined by the venous return volume and peripheral vascular resistance in an organism, the t-point also depends mainly on the venous return volume and peripheral vascular resistance.
Now, assuming that a circulation state in an organism has changed, thus changing the pump speed corresponding to the t-point, the speed increase indicates an increase of the venous return when the blood pressure is unchanged. On the other hand, it indicates an increase of the blood pressure when the venous return is unchanged. The speed decrease indicates vice versa. In other words, since the t-point changes according to the circulation state in an organism, controlling pump speed so as to always exist at the t-point or near the t-point provides circulation assistance that is neither too much nor too little for an organism according to the change in the organism.
Near the t-point means the range that provides practically sufficient accuracy to estimate the change of circulation state in an organism. For example, it is the speed within the range of xc2x12 to 3% of the speed at the t-point.
Controlling the pump speed based on the t-point is an example showing the possibility of the control corresponding to the circulation state in an organism with using the amplitude of flow rate fluctuation such as the amplitude of the motor current consumption fluctuation mentioned here. Therefore, a control base can be selected according to the specific purpose.
In the above description, only the circulation assistance is mentioned. Further it is possible to apply the fluctuation amplitude of consumption current waveform at the t-point or near the t-point to diagnosis of inflow state at a blood inflow portion and filling state in the heart.
The s-point is the point at which the pulsation of blood flow in the pump becomes apparent due to sucking. When the blood inflow portion of the blood removing pipe in the pump has no problem and sucking is unlikely to occur, the amplitude of current value fluctuation is substantially zero at the s-point or near the s-point, reflecting that a continuous flow has been generated in the pump. Therefore, the current amplitude at the s-point can be used for detecting a problem in the blood inflow portion of the blood removing pipe in the pump, such as blood removal failure due to improper location of the blood removing pipe, formation of a thrombosis or other obstructions, or distinctive decrease of blood volume (dehydration or shock), thus controlling blood circulation assistance appropriately. The amplitude of current value fluctuation near the s-point, even if it is not exactly the s-point, provides the control satisfactory enough in an actual use. Near the s-point means the range that provides practically sufficient accuracy to estimate the change of circulation state in an organism. For example, it is the speed within the range of xc2x12 to 3% of the speed at the s-point. In addition, xe2x80x9csubstantially zeroxe2x80x9d described above means the range of current amplitude that can be used for detecting the problems at the s-point or near the s-point and realize an appropriate control of blood circulation assistance.
Also, the s-point or near the s-point is the point at which distinctive sucking does not occur and the heart of an organism generates the lowest pressure. This means that the maximum effect of stress reduction of the heart can be obtained safely. Thus, controlling the pump speed so as to always exist at the s-point or near the s-point realizes the safe and maximum effect of stress reduction of the heart.
As it is clear with the above description, controlling the pump speed so as always to be substantially between the t-point and the s-point realizes the safe and effective circulation assistance, which is neither too much nor too little for an organism and provides the maximum effect of stress reduction of the heart.
Any indicators directed to the measurement parameter, which is influenced by a pulsation of an organism and is reflected on the continuous flow blood pump, can be used in controlling the pump device. In particular, the present invention uses a pulsation amplitude as this indicator for control. Also, when using the current value of a pumping motor, the indicator for control may be a numerical value that is made into an indicator based on a pulsation amplitude of the current value. Specifically, they may be such a value as the one obtained by dividing the amplitude of the current value fluctuation of a pumping motor with a mean current value or the one obtained by dividing the amplitude with a current consumption difference between open operation period and closed operation period at the same pump speed (theoretical maximum amplitude). xe2x80x9cOpen operation periodxe2x80x9d is the case where a pump is operated with the conduit, which is communicated with the outflow portion of the pump, being open. On the contrary, xe2x80x9cclosed operation periodxe2x80x9d is the case where a pump is operated with the conduit being closed.
The present invention does not require the specific sensor such as the one for monitoring a blood character. Mere flow rate measurement can detect blood circulation. The flow rate measurement may be conducted directly with a flow rate sensor or indirectly with other measuring means.
As the indirect measuring means, for example, motor consumption current of a continuous flow blood pump can be used. Consumption current multiplied by voltage makes electric power, so the electric power may also be used. Since consumption current can be obtained as an internal data of a motor, a sensor is not needed, leading to simplification of the device, improvement of reliability and safety, increase of long-term durability, cost reduction, miniaturization, etc.
A direct means of measuring flow rate is a flow rate sensor such as an ultrasonic flow meter. Since it is conventionally used as a sensor, the structure of the device is far simpler than in the case where a specific sensor for monitoring blood characteristics is needed.
The pump used in the present invention may be any continuous flow blood pump and is not limited to a specific pump. The pump may be located either externally or internally, and the assisting period may be either short or long. A blood removal site and a blood feed site are not limited. Assistance may be either in the right ventricle or left ventricle.
As is clearly shown in above description, the present invention may be embodied in various modes in the following that are suitable for actual use, in addition to above basic configurations.
An output corresponding to the flow rate may be obtained by using means for measuring a current consumption or a power consumption value of the motor for the continuous flow blood pump, whereby the flow rate detection means is configured. Alternatively, an output corresponding to the flow rate is obtained by using a flow sensor,disposed near the continuous flow blood pump, whereby the flow rate detection means is configured. In this manner, a simple device can be configured without any specific sensor for monitoring blood characteristics.
Moreover, the flow rate amplitude detection means may be configured so that it detects a maximum value and a minimum value of the output of the flow rate detection means at predetermined time intervals and outputs the maximum and the minimum value. Alternatively, the flow rate amplitude detection means is configured so that it detects a maximum value and a minimum value of the output of the flow rate detection means at predetermined time intervals and outputs a flow rate amplitude that is a difference between the maximum and the minimum values. Alternatively, the flow rate amplitude detection means is configured so that it detects a mean value and a fluctuation amplitude of output of the flow rate detection means at predetermined time intervals and outputs an amplitude index that is obtained by dividing the amplitude with the mean output. In this manner, the desired output according to a control method can be obtained.
Furthermore, the blood circulation assisting device may be configured so that it includes a display means for displaying the output of the flow rate amplitude detection means and a means for manually operating and adjusting a speed of the motor, thereby providing a simple device that easily can perform appropriate blood circulation assistance.
The blood circulation assisting device further may include a means for controlling a speed of the motor for driving the pump according to the output of the flow rate amplitude detection means so that the flow rate amplitude is within a predetermined range. Alternatively, it further includes a means for controlling a speed of the motor for driving the pump according to the output of the flow rate amplitude detection means so that the flow rate amplitude index is within a predetermined range. The above configurations provide a device that performs an automatic control for appropriate blood circulation assistance.
Furthermore, in the above-described device including the means for controlling a speed of the motor according to the output of the flow rate amplitude detection means so that the flow rate amplitude is within the predetermined range, the controlling means may be configured as follows. With the device being attached to an organism, the motor speed of the continuous flow blood pump is changed, so that the t-point at which circulation assistance by the pump changes from partial to total assistance is detected based on an output change of the flow rate amplitude detection means caused by the change of the motor speed. The motor speed is controlled so as to be in a predetermined relationship to the motor speed at the detected t-point. Alternatively, the motor is controlled so as to have a speed at the t-point or near the t-point. In this manner, an optimal operation is realized according to a clinical condition of an organism.
Furthermore, in the above-described device including the means for controlling a speed of the motor according to the output of the flow rate amplitude detection means so that the flow rate amplitude is within the predetermined range, the controlling means may be configured as follows. With the device being attached to an organism, the motor speed is changed, so that the s-point, at which a fluctuation of the flow rate amplitude becomes distinctive because a blood inflow port of the blood removing pipe starts sucking on to a wall of the organism, is detected based on an output change of the flow rate amplitude detection means caused by the change of the motor speed. The motor speed is controlled so as to be in a predetermined relationship to the motor speed at the detected s-point. Alternatively, the s-point is detected similarly based on the flow rate amplitude index, and the motor speed is controlled so as to be in a predetermined relation to the motor speed at the detected s-point. Alternatively, the motor is controlled so as to have a speed corresponding to the speed between near the t-point and near the s-point. Alternatively, a blood circulation is assisted so that the flow rate amplitude at the s-point is as small as possible and substantially zero. Alternatively, the motor speed is controlled so that when the motor speed is changed within a predetermined range, a correlation between the motor speed and index of current amplitude is negative. Above configurations realize a device that provides the safe and maximum stress reduction effect of the heart.
A diagnosis apparatus for blood circulation state includes the blood circulation assisting device described above, and is configured as follows: with the device being attached to an organism, the motor speed of the continuous flow blood pump is changed, so that the t-point at which circulation assistance by the pump changes from partial to total assistance is detected based on an output change of the flow rate amplitude detection means caused by the change of the motor speed. An inflow state at a blood inflow port and/or filling state of a heart are detected based on the flow rate amplitude at the detected t-point or near the t-point. Alternatively, the t-point is detected in a similar manner, so that the change of the motor speed at the detected t-point or near the t-point is detected, and a change of circulation state in the organism is detected with the speed change. Alternatively, in a similar manner, when the motor speed at the t-point or near the t-point increases, unchanged blood pressure is judged as an increase of venous return or unchanged venous return is judged as an increase of blood pressure. On the other hand, when the motor speed at the t-point or near the t-point decreases, unchanged blood pressure is judged as a decrease of venous return or unchanged venous return is judged as a decrease of blood pressure. Above configurations provide a diagnosis apparatus that can easily diagnose blood circulation state in an organism with a simple structure.
Furthermore, the apparatus may be configured by using the above-described blood circulation assisting device, so that the s-point is detected as mentioned above, and an inflow state at the blood inflow port and/or filling state of a heart are detected based on the flow rate amplitude at the detected s-point or near the s-point. Alternatively, the s-point is detected in a similar manner, the speed at the detected s-point or near the s-point is detected, and a change of circulation state in the organism is diagnosed with the speed change. Above configurations realize a diagnosis device for preventing an injury due to sucking from generating.
A blood circulation assisting method in which the blood circulation assisting device with above configuration is attached to the organism to assist blood circulation can easily realize appropriate circulation assistance for a blood circulation state in the organism.
A method for diagnosing an organism in which the diagnosis device with the above configuration is attached to the organism to diagnose a blood circulation state easily can diagnose a blood circulation state in the organism.